1. Center for Energy Research, University of California, San Diego, La Jolla, California 92093, USA
2. Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
3. Lawrence Livermore National Laboratory, Livermore, California 94550, USA
4. Plasma Physics Department, GSI Helmholtzzentrum, Darmstadt D-64291, Germany
5. General Atomics, San Diego, California 92121, USA